KABUL, Afghanistan — A massive explosion rocked a highly secure diplomatic area of Kabul on Wednesday morning, killing 80 people and wounding as many as 350, an attack that left a scene of mayhem and destruction and sent a huge plume of smoke over the Afghan capital.

The target of the attack — which officials said was a suicide car bombing — was not immediately known, but Ismail Kawasi, spokesman of the public health ministry, said most of the casualties were civilians, including women and children.

It was one of the worst attacks Kabul has seen since the drawdown of foreign forces at the end of 2014.